Real-time computerized in situ guidance system for ACL graft placement.

A recent consensus within an international society for sports traumatology revealed that approximately 40% of ACL grafts are being surgically misplaced in current clinical practice. To help solve this problem, a computer-assisted system has been developed at the M.E. Müller Institute for Biomechanics to perform intraoperative planning and guidance of ACL replacement. Dynamic reference bases are fixed on the femur and tibia to track the knee's movement. No intraoperative imaging is required, and potential ligament attachment sites can be directly digitized using a computerized palpation hook in a minimally invasive fashion when used in conjunction with standard endoscopic tools. The palpation hook can be used by the surgeon to interactively define various anatomical structures and reference landmarks that are important for proper ligament positioning. The system can input a standard diagnostic X-ray (sagittal view of the femur) and allows intraoperative registration of this image with the patient to provide valuable X-ray landmarks for intraoperative guidance. The computer helps in situ planning of ligament placement by providing the surgeon with a 3D overview of the relevant anatomical landmarks and information on graft impingement and elongation for various simulated surgical insertions and graft sizes. After planning, the computer helps guide placement of the chosen insertion tunnels. This approach provides an augmented 3D view of knee anatomy and ligament function prior to drilling that is not possible with current procedures. The flexibility of the system in permitting surgeon-defined landmarks and free interpretation of functional factors allows it to support a variety of surgical workflows and techniques.

[Using the CAS (computer-assisted surgery) system in arthroscopic cruciate ligament surgery--adaptation and application in clinical practice]. / Anwendung eines CAS-Systems in der Arthroskopischen Kreuzbandchirurgie--Adaptation und Applikation in der klinischen Praxis.

AIM AND METHOD: The anterior cruciate ligament (ACL) is of great importance for the knee joint function. In the case of a complete ligament injury there is hardly any chance for complete recovery. The clear advantages of an operative reconstruction by replacing the ACL has been shown in many trails. The accurate placement of the graft's insertions has a significant effect on the mid- and probably long-term outcome of this procedure. Reviewing the literature, there are poor long-term results of ACL replacement in 5 to 52% of all cases, depending on the score system. One of the main reasons for unacceptable results is graft misplacement. This led to the construction of a CAS system for ACL replacement. The system assists this surgical procedure by navigating the exact position of the drilling holes. The Potential deformation quantity of the transplant can be controlled by this system in real time. RESULTS: 40 computer-assisted ACL replacements have been performed under active use of the CAS system. The short-term results are encouraging, no special complications have been seen so far. Prospective long-term follow-up studies are ongoing. CONCLUSION: ACL reconstruction by manual devices has many sources of error. The CAS system is able to give the surgeon reasonable views that are unachieveable by conventional surgery. He is therefore able to control a source of error and to optimise the results. The feasibility of this device in clinical routine use has been proven.

Animation of in vitro biomechanical tests.

Interdisciplinary communication of three-dimensional kinematic data arising from in vitro biomechanical tests is challenging. Complex kinematic representations such as the helical axes of motion (HAM) add to the challenge. The difficulty increases further when other quantities (i.e. load or tissue strain data) are combined with the kinematic data. The objectives of this study were to develop a method to graphically replay and animate in vitro biomechanical tests including HAM data. This will allow intuitive interpretation of kinematic and other data independent of the viewer's area of expertise. The value of this method was verified with a biomechanical test investigating load-sharing of the cervical spine. Three 3.0 mm aluminium spheres were glued to each of the two vertebrae from a C2-3 segment of a human cervical spine. Before the biomechanical tests, CT scans were made of the specimen (slice thickness=1.0 mm and slice spacing=1.5 mm). The specimens were subjected to right axial torsion moments (2.0 Nm). Strain rosettes mounted to the anterior surface of the C3 vertebral body and bilaterally beneath the facet joints on C3 were used to estimate the force flow through the specimen. The locations of the aluminium spheres were digitised using a space pointer and the motion analysis system. Kinematics were measured using an optoelectronic motion analysis system. HAMs were calculated to describe the specimen kinematics. The digitised aluminium sphere locations were used to match the CT and biomechanical test data (RMS errors between the CT and experimental points were less than 1.0 mm). The biomechanical tests were "replayed" by animating reconstructed CT models in accordance with the recorded experimental kinematics, using custom software. The animated test replays allowed intuitive analysis of the kinematic data in relation to the strain data. This technique improves the ability of experts from disparate backgrounds to interpret and discuss this type of biomechanical data.

Novel computer-assisted fluoroscopy system for intraoperative guidance: feasibility study for distal locking of femoral nails.

OBJECTIVES: Orthopaedic procedures that use fluoroscopy require intraoperative mental navigation of the surgical tools in a three-dimensional space. Moreover, because of their reliance on real-time monitoring, such procedures are frequently associated with increased x-ray exposure. The goal of this study was to develop a computer-guided surgical navigation system based on fluoroscopic images that not only facilitates direction of surgical tools within anatomy, but also provides constant feedback without the need for radiologic updates. To evaluate the feasibility of the new technology, the authors used it on cases requiring distal locking of femoral nails. METHODS: The hardware components of the system include an instrumented C-arm, optoelectronic position sensor, stereotactic tools, and custom-made software. Computer integration of these devices permitted C-arm alignment assistance and real-time navigation control without constant x-ray exposure. The nails were locked in a variety of media, including plastic femurs, dry human femoral specimens, human cadavers, and one clinical case. Unreamed femoral nail sizes ranged from 9/340 to 12/400. Radiographs were taken to confirm that screws were positioned correctly, and fluoroscopic time associated with the locking procedure was recorded. RESULTS: All distal holes were locked successfully. In eight (11 percent) of seventy-six holes, the drill bit touched the canal of the locking hole, albeit with no damage to the nail and no clinical consequences. The fluoroscopy time per pair of screws was 1.67 seconds. CONCLUSIONS: The developed system enables the physician to precisely navigate surgical instruments throughout the anatomy using just a few computer-calibrated radiographic images. The total radiation time per procedure can be significantly reduced because additional x-ray exposure is not required for tool navigation.

Computer-assisted fluoroscopy-based reduction of femoral fractures and antetorsion correction.

OBJECTIVE: Intra-operative fluoroscopy is a valuable tool for visualizing underlying bone, implant, and surgical tool positions in orthopedics. It has brought about the minimally invasive surgical technique of intramedullar nailing to fix femoral shaft fractures. However, the limited field of view and two-dimensional property of fluoroscopic images aggravate intra-operative control of surgical parameters. The purpose of this article is to introduce a surgical navigation system based on fluoroscopy that provides missing information for the procedure of femoral fracture fixation. MATERIALS AND METHODS: Optoelectronic markers are placed on a surgical drill, involved bone fragments, the femoral nail, and the fluoroscope to track their positions. Projection properties of the fluoroscope are acquired through an initial precalibration. The relative positions of bone fragments, implants, and surgical tools are displayed superimposed simultaneously and in real time on multi-planar intra-operative fluoroscopic images. This is achieved by computer simulation of X-ray projections that have taken place with acquisition of the fluoroscopic images. In addition, a method has been developed that allows contactless measurement of three-dimensional anatomic landmarks, based on their representation in fluoroscopic images. In combination with optoelectronic tracking, this enables dynamic calculation of important surgical parameters such as femoral antetorsion. RESULTS: A pilot surgery showed that fracture reduction can benefit from the developed computer-assisted method. An in-vitro study on computer-assisted measurement of femoral antetorsion demonstrated the high degree of precision of this technique.

Fluoroscopy as an imaging means for computer-assisted surgical navigation.

OBJECTIVE: Intraoperative fluoroscopy is a valuable tool for visualizing underlying bone and surgical tool positions in orthopedic procedures. Disadvantages of this technology include the need for continued radiation exposure for visual control, and cumbersome means of alignment. The purpose of this article was to highlight a new concept for a computer-assisted freehand navigation system that uses single intraoperatively acquired fluoroscopic images as a basis for real-time navigation of surgical tools. MATERIALS AND METHODS: Optoelectronic markers are placed on surgical tools, a patient reference, and the fluoroscope to track their position in space. Projection properties of the fluoroscope are acquired through an initial precalibration procedure using a tracked radiopaque phantom grid. Corrections are applied to compensate for both the fluoroscope's image intensifier distortions and the mechanical bending of the C-arm frame. This enables real-time simulation of surgical tool positions simultaneously in several single-shot fluoroscopic images. In addition, through optoelectronically tracked digitization of a target viewpoint, the fluoroscope can be numerically aligned at precise angles relative to the patient without any X-ray exposure. RESULTS: This article shows the feasibility of this technology through its use in cadaver trials to perform the difficult task of distal locking of femoral nails.

Computer assisted knee surgery: diagnostics and planning of knee surgery.

Cruciate ligament rupture, a common injury among young active adults, disrupts the knee's complex movement and often leads to premature degenerative arthritis of the joint. Prosthetic cruciate ligaments can be used for replacement but often fail owing to incorrect surgical placement. To aid in the planning of cruciate prosthetic substitution, a computerized system has been developed to provide the surgeon with a virtual interface allowing accurate visualization of three-dimensional (3D) bone structure and movement normally hidden beneath layers of soft tissue. Preoperatively, precise in vivo kinematics are quantified with the help of 3D medical images. Three-dimensional imagery techniques based on computed tomography (CT) have been developed to obtain accurate 3D reconstruction of knee geometry preoperatively. The system allows the surgeon to know the real-time spatial position of the patient via magnetic position and orientation sensors attached noninvasively onto the femur and tibia via a new attachment system. An interactive computer program has been developed to allow the user to simulate different prosthetic ligament insertions and compute elongation, bending, and torsion values that will be imposed on the prosthesis. Through comparison with cadaver studies and a perturbation analysis, the system is shown to be sufficiently accurate to predict certain in vivo ligament bending and torsion deformations.

Computer-assisted pedicle screw fixation. A feasibility study.

STUDY DESIGN: We evaluated a computer-assisted surgical tool for inserting pedicle screws. OBJECTIVES: This study reviewed the feasibility, usefulness, and accuracy of the proposed tool. SUMMARY OF BACKGROUND DATA: Reviews documented neurovascular damage caused by screw misplacement. Currently, screw hole position is assessed by radiologic means and curette palpation. METHODS: Three sheep vertebrae and one artificial object were reconstructed three-dimensionally from computed tomography scan slices. At surgery, the surgeon's movements were displayed relative to the three-dimensional vertebrae on a computer screen. The tool was used to detect pedicles and to verify the position of drilled holes. In our laboratory, we calculated the system's accuracy by taking measurements on the artificial object. RESULTS: All pedicles were identified with the computer. Five of the six drilled hole positions were correctly represented. An accuracy of 4.5 mm +/- 1.1 mm RMS (root of the mean squared) and 1.6 degrees +/- 1.2 degrees were calculated. CONCLUSIONS: Results suggested the proposed system could be useful for pedicle detection and assessing the intravertebral location of a drilled hole. The proposed system could be used for many different orthopedic procedures where structures are hidden from the surgeon's view.

A simple algorithm for measuring the concavity/convexity ratio and lobe counting of a closed curve. With a review of the literature on form factors measuring concavity.

The algorithm described here identifies concave and convex segments of a closed contour by vector algebra, thereby defining the shape of a two-dimensional object in multiple ways: (1) as a ratio of total concave vs. total convex periphery length, (2) as the number of convexity changes per unit of perimeter length (or number of lobes per contour), (3) as the mean +/- SD of convex and/or concave segment lengths, and (4) as a measure of the discrete curvature from a finite number of points on the contour. The algorithm can be used, in its capacity to distinguish regularity and amplitude of indentations ("wrinkles" and "lobes"), in studies where the number, regularity and magnitude of surface fluctuations are important differentiating morphologic characteristics of the object. This short algorithm can easily be integrated among other classic algorithms measuring periphery, area, shortest and longest diameter, and form factors derived therefrom. The possibility of automating this method makes it possibly useful for the discrimination of shapes by artificial vision.